Asymptomatic school-age children carry the majority of transmissible Plasmodium falciparum infections

Background
Persistent human-to-mosquito parasite transmission hinders malaria control in high burden settings. Understanding the human transmission reservoir can support the design of targeted interventions to reduce transmission.

Methods
In a year-long cohort study in rural Malawi, we used molecular methods to detect all Plasmodium falciparum (Pf) infections and those containing gametocytes, the parasite stage required for transmission, longitudinally at routine surveillance and sick visits. Using population-level analyses, we determined the demographic, temporal, and spatial clustering of infections containing gametocytes and gametocyte density, which predicts transmission.

Results
Here we show that gametocytes are not randomly distributed among the population or among individuals with Pf infections; gametocytes are detected in only 23% of the population. Among all participants, school-age children have significantly higher incidence of gametocyte-containing infections and high-density gametocyte infections compared to other groups. The presence of school-age children is a key driver of gametocyte frequencies and densities within households, even after adjusting for Pf infection levels. Based on the total gametocyte abundance in the population, we estimate that clearing infections from asymptomatic school-age children in the rainy season would decrease gametocyte abundance by 67% in the population.

Conclusions
School-age children are the primary driver of ongoing Pf transmission in Malawi and interventions targeting school-age children are needed to effectively reduce Pf infection risk at a population level.